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Date: Tue, 8 Jul 2008 21:47:22 +1000 (EST)
From: Bruce Evans <brde@optusnet.com.au>
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To: Erik Trulsson <ertr1013@student.uu.se>
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Cc: FreeBSD Net <freebsd-net@FreeBSD.org>, Andre Oppermann <andre@FreeBSD.org>,
	Ingo Flaschberger <if@xip.at>, Paul <paul@gtcomm.net>
Subject: Re: Freebsd IP Forwarding performance (question, and some info)
 [7-stable, current, em, smp]
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On Mon, 7 Jul 2008, Erik Trulsson wrote:

> On Mon, Jul 07, 2008 at 10:30:53PM +1000, Bruce Evans wrote:
>> On Mon, 7 Jul 2008, Andre Oppermann wrote:
>>> The theoretical maximum at 64byte frames is 1,488,100.  I've looked
>>> up my notes the 1.244Mpps number can be ajusted to 1.488Mpps.
>>
>> Where is the extra?  I still get 1.644736 Mpps (10^9/(8*64+96)).
>> 1.488095 is for 64 bits extra (10^9/(8*64+96+64)).
>
> A standard ethernet frame (on the wire) consists of:
> 7 octets preamble
> 1 octet  Start Frame Delimiter
> 6 octets destination address
> 6 octets source address
> 2 octets length/type
> 46-1500 octets  data (+padding if needed)
> 4 octets Frame Check Sequence
>
> Followed by (at least) 96 bits interFrameGap, before the next frame starts.
>
> For minimal packet size this gives a maximum packet rate at 1Gbit/s of
> 1e9/((7+1+6+6+2+46+4)*8+96)/ = 1488095 packets/second
>
> You probably missed the preamble and start frame delimiter in your
> calculation.

Thanks.  Yes, that was it.

Bruce